Synchronized control system



June 4, 1963 A. H. SMITH 3,092,756

SYNCHRONIZED CONTROL SYSTEM Filed Dec. 11, 1959 5 Sheets-Sheet 1 INVENTOR. Humav H, Smn'u flue, Mm, bmwyzs i HTToRNEyS June 4, 1963 A. H. SMITH 3,092,756

SYNCHRONIZED CONTROL SYSTEM Filed Dec. 11, 1959 3 Sheets-Sheet 2 MHSTER DRIVE f) SLRVE DRIVE H-C. SOURCE INVENTOR. Huanav H. SMiTH June 4, 1963 A. H. SMITH SYNCHRONIZED CONTROL SYSTEM 3 Sheets-Sheet 5 Filed Dec. 11, 1959 INVENTOR. HuBRsY H. SMiTH flas M 1 RTT RN YS 3,092,756 SYNCHRONIZED CONTROL SYSTEM Aubrey H. Smith, Kenosha, Wis, assignor to Eaton Manufacturing Company, Cleveland, Ohio, at corporation of Ohio Filed Dec. 11, 1959, Ser. No. 859,013 11 Claims. (Cl. 317-6) This invention relates to a control system for governing in a highly accurate manner the operating characteristics of a plurality of drives including a master drive and a slave drive, and more particularly to a synchronized pre drive control system and mechanism for such environmental equipment as news-print and magazine press automatic paster drives, sectional processing machinery, sectional power driven conveyor systems and the like.

The problem of making automatic pastes or flying splices on paper stock being fed into printing presses is critical and depends upon the adhesive used, the preparation of the new roll of paper stock, and the relative velocity between the paper being fed into the press from a first nearly exhausted supply roll and the paper on the next or upcoming supply roll, which is adapted to be spliced to the terminal end of the paper on the first supply roll upon exhaustion of the latter, and without stopping the press operation.

If the peripheral speed of the paper on the upcoming or new supply roll exceeds the paper velocity from the used supply roll, upon splicing thereof, the new roll will have a relatively high inertia, and will continue to pay oii paper faster than the press is using it, which results in a droop in the paper between the new roll and the press, thereby allowing the paper to whip ahead of the supply roll and become torn. On the other hand if the peripheral velocity of the new supply roll is less than the paper passing through the press from the used supply roll, upon splicing thereof, the inertia of the new roll will have to be accelerated by the paper passing through the press which in turn increases the tension of the paper between the new roll and the press, again resulting in tearing of the paper.

The present invention provides a novel control system for precisely synchronizing the speed and phase of a master drive which may govern for instance the speed of paper fed to a press, and a slave drive which may be adapted to govern the peripheral speed of an upcoming supply roll of paper stock, to thereby permit a flying splice on the paper without danger of tearing thereof, and which embodies braking means operative in response to deceleration of the master drive, for decelerating the slave drive in precise synchronism with the master drive, to thus precisely control in an optimum manner the peripheral speed of the new or upcoming roll of paper stock. inventive concept of the control system will be illustrated and described in the environmental setting of printing press machinery, it may be readily adapted for use with other environmental mechanism as tor instance those of the aforementioned types.

Accordingly, an object of the invention is to provide a novel control system for governing in a highly accurate manner the operating characteristics of a plurality of drives including a master drive and a slave drive, adapted to operate in synchronism with the master drive.

Another object of the invention is to provide a control system of the latter type including means for speed and phase synchronization of the slave drive in response to acceleration of the master drive, and other means for speed and phase synchronization of the slave drive in response to deceleration of the master drive.

A still further object of the invention is to provide a simplified, more economical control system of the above It will be understood of course that while the.

dfidzfifid Patented June 4-, 1963 type which is particularly well adapted for use in newsprint and magazine press mechanisms and the like, for permitting flying splices of paper stock from a used, nearly exhausted supply roll of paper with a new or up coming supply roll.

Briefly, the foregoing and other objects and advantages are accomplished in accordance with the invention by providing a multiple-drive system including a master drive and a slave drive, each having associated therewith signal producing means such as a tachometer generator, for producing a signal proportional to corresponding drive speed. Means are provided for comparing the output from the tachometer generators to produce a control signal proportional to the algebraic sum of their outputs. The slave drive embodies an eddy current coupling means together with adjustable electro-responsive means for energizing the eddy current coupling, and a control circuit is provided responsive to the applied aforementioned con trol signal to vary the energization of the eddy current coupling in response to acceleration of the main or master drive. Servo means are provided coacting between these drives to detect and produce a signal proportional to the angular displacement between the drives together with means for combining the last mentioned signal with the signal output from the master tach generator to modify the latter generator signal in accordance with the angular displacement between the drives and thereby provide for the precise speed control of the drives during acceleration and including braking means operative in response to deceleration of the main drive for decelerating the slave drive in precise synchronism therewith.

In the drawings:

FIG. 1 is a combined diagrammatic and schematic illustration of a master-slave drive system including a control system for maintaining the drives in speed and phase synchronization during acceleration and deceleration of the main drive and is illustrated in the environmental setting of a printing press.

FIG. 2 is a diagrammatic block diagram illustrating a modification of the system illustrated in FIG. 1 and more particularly a system which utilizes a more or less mechanical control arrangement for providing for the precise or fine speed matching of the drives as opposed to the strictly electrical control arrangement for accomplishing the same end result and as is utilized in the FIG. 1 system.

FIG. 3 is a schematic illustration of the control portion of the system illustrated in FIG. 2.

Referring now to FIG. 1 of the drawings, there is diagrammatically and schematically illustrated an environ mental printing-press setting in which the present invention is particularly well adapted for use. Paper stock 10 is being fed from supply roll A rotatably mounted on yoke structure 12, which in turn is adapted for rotation in the direction of the arrow shown, so that a new or unused supply roll B of paper stock may be readily presented for convenient splicing of the new roll B to the terminal end of the paper on roll A, upon exhaustion of the latter, and without stopping or terminating the operation of the press.

The paper from the active supply roll is fed over guide roller 14 and over a power driven roller 16 to the press prop-er, with the power roller 16 being driven by a master or main drive including a variable speed electric motor (not shown) preferably having a variable speed ratio in excess of to l. A common shaft 18 is provided which is drivingly coupled to the motor of the master drive and to the roll 16, and a tachometer generator 20 is mounted on shaft 18 for use in synchronizing the master drive with a slave drive, referred to generally by reference number 22, and as will be hereinafter described, together with its operation. Shaft 18 is also coupled to a selsyn signal sin or transmitter generator 24, via any suitable gear means 26 in the conventional manner.

The rotor 24a of selsyn generator 24 is coupled to the gear means 26, and the field or stator 24!) of generator 24 is coupled to the field or stator of a selsyn or control generator 28 coupled to a common shaft 36' of the slave drive uni-t 22. The purpose of selsyn generators 24 and 28 is to provide for the fine or close speed matching of the drives and as will hereinafter be discussed in detail.

The slave drive unit 22 is adapted to actuate the new supply roll B to a peripheral speed similar to the speed of the paper 110 being fed through the press so as to prevent tearing of the paper upon a flying splice of the paper stock from for instance new roll B to the exhausted roll A.

Slave drive unit 22 comprises a constant speed motor 32 which is drivingly coupled to a drum 34 comprising a component part of an eddy current slip clutch 36. The drum 34 is adapted for eddy-current coupling in a conventional manner with the rotor member 33 of eddy current clutch 36, and which includes a field coil 46; the rotor member and field coil being coupled to the common shaft 30. Mounted in secured relation on shaft 31 is a torque transmitting pulley or roller 42 which transunits torque from shaft 30 to the new paper stock roll B, and via belt 44 and idler pulley 46.

It will be seen from FIG. 1 that both a side and end view of pulley 42 has been shown in the interest of clarity, it being understood that the supply rolls and associated yoke are shown in end view to better illustrate the passage of the paper stock from the supply rolls through the press. As will be understood by those skilled in the art, the amount of torque transmitted from the drum 34 of the eddy-current slip clutch 36 will be pro portional to the current through the clutch field coil 4-0.

Also mounted in secured relation on the common shaft 30 of the slave drive 22 is a braking mechanism 43 comprising an external brake drum element 44 which is adapted for braking coaction with braking elements or shoes 46 including actuating coil 46a, for exerting a retarding torque on the shaft and consequent retarding torque on roll B in a similar but reverse manner as the acceleration torque transmitted by the eddy-current clutch 36.

A tachometer generator 48 is also mounted on common shaft 36 and generates an AC. voltage directly proportional to the velocity of roll 42, while tachometer generator 2d of the master drive generates an AC. voltage directly proportional to the velocity of driven roll 16, the latter measuring the velocity of the paper 16 passing through the press.

The voltage from tachometer generator 2% of the main drive is rectified, doubled and filtered by rectifiers 50 and 52, resistors 54- and 56, and condensers 58 and 6th, and an adjustable potentiometer 62 feeds a DC. voltage proportional to the velocity of roll 16 (and the velocity of the paper It) passing through the press) into a clutch amplifier circuit generally referred to by reference number 64, so that such voltage is negative at terminal B and positive at terminal E of a transistor element 66, and thus causing the transistor 66 to conduct.

The AC. voltage from tachometer generator 43 on the slave drive 22 is fed via feed lines 68 into the clutch amplifier circuit 64, rectified, doubled and filtered by rectifiers 79 and 70a, resistors 72 and 72a, and capacitors 74 and 74a, and then fed into terminal B of transistor 66, so that it is positive at B and negative at terminal E, or in other words opposite to the voltage being fed from potentiometer 62, thereby tending to cause the transistor 66 not to conduct.

When transistor 66 does conduct, a voltage drop ocours across resistors 76 and '78 in the clutch amplified circuit 64 so that the voltage applied to the transistor Si is negative at B with respect to its terminal E. Transistor 80 then conducts current, coming from a DC.

4 power source comprising rectifiers S2 and 82a and transformer 84, the primary 84a of which is connected via lines 86 to power supply lines L and L to lines 68 and thence to the coil 40 of the eddy-current slip clutch 36, thereby causing torque at roller 42.

If roller 42 and power driven roller 16 have the same diameter and power driven roller 16 is rotating at a velocity V, then maximum available torque of the mechanical system will be applied to roll 42 and until the latter approaches the velocity V of power roll 16. Then tachometer generator 48 will reduce the conduction of transistor element until the torque at roll 42 exactly equals the torque of windage and friction of the system.

Since transistor element 8%) must conduct some to' maintain torque equilibrium, the velocity of roll 42 will be equal to the aforementioned velocity V minus some small increment of velocity.

To compensate for this relatively small error in the velocity of roll 42, aforementioned selsyn or transmitting generators 24 and 23 are introduced into the system to thereby provide an extremely close or fine speed matching of the main :and slave drives. Selsyn 24 has its rotor 24a connected across the primary side 90:; of transformer 96 disposed in the brake amplifier circuit, the latter circuit being generally referred to by reference number 92, and with such transformer 96* being connected to the aforementioned power supply lines L and L The stator windings 24b of selsyn 24 are connected as aforementioned to the stator windings 28b of selsyn 23 in the slave drive unit 22. The rotor 28a of selsyn 28'is drivingly coupled to common shaft 30 via conventional gear means 93 and has its winding connected in series with the secondary 96a of a transformer 96, and since the primary coil 96b of transformer 96 is coupled to power supply lines L and L by feed lines 86, and since the rotor 24a of selsyn 24 is also connected to the same feed lines 86, the output of transformer 96 is of the same phase thatis being fed to the rotor 24a of selsyn 24 via lines 97.

When roll 42 and roll 16 are indexed to a reference point or, in other Words, the reference point that is the electrical zero of rotor 28a of selsyn 28 and the rotor 24a of selsyn 24, the rotor voltage of rotor 28a is zero. However, when roll 42 lags behind the reference point, or in other words lags behind the speed of roll 16, the voltage from rotor 28a of selsyn 28 is proportional to the angle of lag and yet is in phase with the voltage from transformer 96, and when roller 42 leads the reference point, the voltage fromrotor 26a of selsyn 28 is proportional to the angle of lead and 180 degrees out of phase with the voltage of transformer 96.

Accordingly, the voltage that appears at points X and Y in the circuit is the sum of the voltage of transformer 96 and the rotor 28a of selsyn 28, and comprises a constant voltage E plus or minus a variable voltage 2 depending upon the angle of lead or lag between rolls 42 and 16.

The voltage at points X and Y is rectified and filtered by rectifiers 1%, 100a, limb and 100C, resistor 102 and capacitor 164, so that the DC. voltage across the potentiometer 166 is proportional to the voltage at points X and Y.

The potential from potentiometer 166 is combined with the potential from potentiometer 62, so that it calls for a velocity increase.

Since the transformer 96 produces a constant voltage across the potentiometer 106, potentiometer 196 is always calling for a higher speed than potentiometer 62, regardless of the angular relations between rolls 42 and 16. Therefore, with zero voltage output from the rotor 28a of selsyn 23, a bias network in the clutch amplifier circuit 64, comprising a secondary winding 168' of aforementioned transformer 84, rectifier 11d, capacitor 112, aforementioned resistor 78 and resistors 114, 116 and 113,

O and adjustable potentiometer 120, is adjusted to balance the fixed voltage produced by transformer 96.

With such an arrangement, if rollers 42 and 16 are angularly aligned, the control selsyn 28 does not provide a corrective signal, and speed tachometers 48 and 20 provide the intelligence for synchronizing rolls 42 and 16. However, when roll 42 leads or lags roll 16, an acceleration or deceleration signal respectively from selsyn 28 will cause roll 42 to again synchronize with roll 16.

Up to this point the description has been concerned with a control providing for positive accelerations of the press, and relatively steady state or continuous constant speed of the master drive of the press. However, dur ing negative accelerations, or in other words deceleration of the master drive of the press, the inertia of supply roll B will cause the roll to continue at its last known velocity, with the only negative torque applied to roll B being the friction and windage in the system, which is insufiicient to keep roller 42 synchronized with power roll 16.

Accordingly, the aforementioned electro-magnetic brake 43 and its associated brake amplifier circuit 92, is provided for furnishing the necessary negative torque to synchronize roll 42 and roll 16 during negative accelerations, or in other words deceleration of the press and associated power roll 16. It will be apparent that negative torque or brake torque is required only when positive torque or clutch torque is not required, and only during deceleration of the master drive of the press.

To provide for the latter braking torque, an adjustable resistor 122 is coupled in series with the clutch coil 41). When current flows through the clutch coil, a ripple is produced across resistor 122. This current ripple is stepped up by transformer 124 and rectified and filtered by rectifiers 126 and 128, resistors 130 and 132, and capacitors 134 and 136. The ripple voltage is then applied to a transistor 141} which is positive at its terminal B with respect to terminal E, thereby cutting off the current flow through the transistors 140, 142 and thus cutting oif the brake coil 46:: from the DC. power source. The latter power source comprises the transformer 96 and rectifiers 144 and 146.

A bias supply consisting of a secondary winding 147 of transformer 90, rectifier 148, capacitor 150, resistors 152, 154, i156 and 158, provides a voltage across a potentiometer 160, such voltage being negative at terminal B with respect to terminal E of the transistor 140, which will tend to cause current to flow in the brake coil. The brake circuit is adjusted by means of the potentiometer 160 so that current in the brake coil is proportional to a constant minus the current in the clutch coil.

It will be seen therefore that when the brake is off the clutch is on and that when the brake is on the clutch is off to thereby provide a system which accurately governs both negative and positive torque to roller 42 to thus synchronize rollers 42 and 16 during negative and positive accelerations of the master drive of the press and thus allowing reliable automatic splices during all operating conditions of the press.

Referring now to FIGS. 2 and 3 of the drawings, there is shown a modification of the system as illustrated in FIG. 1. In FIG. 2, the control is illustrated in a block diagram form for simplicity and in brief, the DC. tachometer generator 162 on the main or master drive provides a reference signal for the clutch amplifier circuit 163. This signal would normally call for maximum speed out of the eddy current clutch 165. However, when the tachometer generator 164 on the slave drive slowly matches the speed of the DC. tachometer generator 162 on the master drive, the excitation of the eddy current clutch 165 diminishes in amounts proportional to the differential end voltage of the DC. tachometer generator on the master drive and the DC. tachometer generator on the slave drive and the output of the clutch amplifier circuit 163. These two signals from the tachometer generators 162,, 164 produce a coarse speed matching.

When the speed of the master and slave drives are closely matched in coarse adjustment, the differential switch 166 detects this close speed matching and cuts in the servo generators 168 and 171 on the main and slave drives respectively. The differential indicator 172 (in the form of a servo generator) and associated potentiometer 176 then takes over to make minute adjustments which are algebraically added to the DC. tachometer generator voltage on the master drive. If the speeds of the servo generators 163, 176 are synchronous, the ditferential indicator 172 will not move its associated potentiometer 176 and no signal change will be applied to adjust the speed of the slave drive. If there is a difference in speed of the two servo generators 168 and 170, the differential generator 172 will rotate to actuate potentiometer 176 and thus adding or subtracting a signal to the DC. tachometer generator on the master drive thus calling, by way of the eddy current clutch on the slave, for the slave drive to either increase or decrease its speed to again bring the servo generators 168, 171) to a synchronous speed.

The brake amplifier circuit 177 receives its signal from the clutch amplifier circuit. When the system is calling for a decrease in speed or in other words during deceleration of the master drive, and the clutch excitation is completely removed from the slave drive, the brake amplifier circuit applies maximum current to the eddy current brake 182 providing a deceleration means to keep the slave unit accurately synchronized with the master drive unit during deceleration or decrease in load on the master drive. The speed relation between the master drive and the slave drive will remain synchronous with the exception that during transients, such as load and speed changes, it is possible to get angular displacement between the shaft 184 of the master drive and the shaft 186 of the slave drive. If however the master drive is running at a given or constant speed and it is required that the slave drive accelerate and overtake the master drive and synchronize with it, the differential switch will cut selsyn or servo generators 168, out until the DC. tachometer generator 162 on the master and the tachometer generator 164 on the slave are closely matched in speed again, and then will cut back in the servo generators 163, 1711 to re-synchronize the system in precise phase and speed matching.

The control portion of the modified system of FIG. 2, excluding the master and slave drives and the eddy-current clutch and brake, is schematically shown in greater detail in FIG. 3 of the drawings. It includes the clutch and brake amplifier circuits, indicated respectively at 163 and 177 within the dotted line blocks, a power supply and differential switch indicated generally within the dotted line block 161, the master and slave tachometer generators 162 and 164, the master and slave servo generators 168 and 1711 and the differential indicator :172 together with the fine adjustment potentiometer 176.

The clutch and brake amplifier circuits are well known and are similar in design and operation. Thus, each amplifier circuit includes a t'hyratron and 175A respectively which are controlled by applying a voltage to the grids which lags the anode voltage by 70 to 90 and is in series with a variable DC. voltage with respect to the cathode. In the clutch amplifier circuit the network including resistors 190, 192, 194 and 196 and rectifiers 198 and 209 may 'be considered as a battery to provide the aforementioned variable DC. voltage through the potentiometer 202. A corresponding variable DC. voltage network is shown in the brake amplifier circuit where like numerals designate like parts except that they are distinguished by the letter A.

In the clutch amplifier circuit, the slave tachometer generator 164 produces a voltage proportional to speed which is rectified by the rectifier 204, filtered by condenser 206 and dropped across resistance 208. The polarity at this point is such as to oppose the variable DC. voltage from potentiometer 202 and thereby reduce the fiow of current through the thyratron 175. The grid voltage which lags the thyratron anode is produced by the resistance of the reference network 1%, 192, 19 i, 1%, are and 211 and condenser 2'12 which is virtually an R.-C. network across the line voltage. The reference voltage is modified by the control signal from the master tachometer generator res for coarse speed matching in the manner hereinbefore described to control the current through the clutch coil 165. Further modification of the reference voltage is accomplished in accordance with this invention to provide fine speed matching when the master and slave servo generators 168 and 17% are energized and their differential output is applied to the differential indicator 172 which adjusts the potentiometer 176 in a direction to correct for the small difference in speed of the master and slave drives. The adjustments at the potentiometer 176 are algebraically added to the master tachometer generator voitage to accomplish the fine speed adjustment. Energization of the servo generators 168 and 17% is accomplished by means of the aforementioned differential switch 166 which measures the difference between the slave tachometer generator voltage and the reference voltage to close the contact 229 to complete the servo-system. Referring now in particular to FIG. 3, the aforementioned differential switch comprises as component parts the normally closed contact 22%, the relay coil 222, and thyratron 224. The tiyratron is triggered by a positive voltage so that relay 222 is energized, and when the latter occurs, the contact 22% is opened and the servo system is not effective. Therefore, when the reference voltage from pctentiometer 202 is greater than the voltage fed back from governor or tachometer generator 164, the voltage is positive on the grid of the thyratron 224-, causing it to conduct. As generator 164 increases in velocity to produce a voltage close to the reference voltage out of potentiometer 176, the grid of the thyratron 224 will go negative and cease conducting. The relay 222 is then de-energized closing its contact 22d and thus as aforementioned causing the servo-system to become effective.

Referring now again to FIG. 3, manual contact means R1 and R2 are provided for de-energizing the self-synchronous system when the machine is not in operation. Such contact means may take the form of a knife switch, relay switch, or any like switch arrangement, and may be either manually or automatically operated in a known manner, depending upon the personal desire of the machine operator.

The brake amplifier circuit 177 receives its signal from the clutch amplifier through the coupling 215. When the system is calling for a decrease in speed the clutch excitation is completely removed and the signal voltage across resistance ZilfiA which ordinarily opposes the variable DC. voltage fromthe potentiometer 292A. is reduced to a minimum and the brake amplifier applies a maximum current to the eddy-current brake coil 132; Thus, the brake decelerates the slave drive to maintain synchronism with the master drive during deceleration transients or decreases in load on the slave drive.

Thus, there have been provided alternative control systems for maintaining the speed of a slave drive in synchronism with a master drive wherein acceleration of the slave drive is accomplished through a coarse and a fine adjustment of the excitation of the eddy-current coupling between the drives. In each arrangement, the coarse adjustment is accomplished by comparing voltages proportional to the speed of each drive and utilizing the differential result to control the excitation of the eddy-current coupling. The fine adjustment is accomplished by algebraically adding a differential signal from a sensitive selsyn system, whose rotors are coupled respectively to the different drives, to the voltage proportional to the speed of the master drive and thereby superimposing a finer adjustment on the control of the eddy-current coupling. The operating level for the control circuits in each arrangement is such that the fine adjustment is not effective until the differential result of the coarse comparison attains an optimum minimum. A control signal proportional to the excitation of the eddy-current coupling automatically de-activates the exciting circuit of an eddy-current brake which only becomes active when the deceleration of the slave drive is required and no excitation is applied to the eddy-current coupling.

I have shown and described what I consider to be the preferred embodiments of my invention along with suggestions of modified forms, and it will be obvious to those skilled in the art that other changes and modifications may be made without departing from the scope of my invention as defined by the appended claims.

I claim:

1. In a system having a variable speed master drive and a slave drive adapted to be coupled to a load and including an electromagnetic coupling between the slave and the load and an electro-magnetic brake for the slave, the coupling and the brake each having a controlled excitation circuit to maintain the slave output in synchronism with the master, the combination comprising, means conditioning the brake excitation circuit to continuously activate the brake, other means operative in response to and during excitation of the coupling to disable the brake excitation circuit, individual means for generating a voltage proportional to the output speed of each drive respectively, means in said coupling excitation circuit for comparing the generated voltages, other means in said coupling excitation circuit for adjusting the excitation of the coupling in accordance with the compared differential voltage between said generated voltages to provide a coarse speed matching of the drives, a servo system coacting between the drives to provide a signal proportional to minute differences in speed between the drives, means for algebraically adding said signal to the voltage generated proportional to the output speed of the master drive and thereby superimpose a fine adjustment on said excitation adjustment means to synchronize the output of the slave with the master.

2. The system of claim 1 wherein said servo system includes a pair of selsyns each having a rotor and a stator winding, said selsyns having their rotors drivingly coupled to the output of. the main and slave drives respectively and having their stator windings interconnected, whereby the selsyn'coupled to the main drive coacts as a transmitter and the selsyn coupled to the slave coacts-as a control transformer in the servo system to detect and produce a control signal corresponding to the angular displacement between the drives. 3. The system of claim 1 wherein said voltage comparmg means includes a governing circuit for converting the voltage generated by the slave drive into a DC. control voltage and a reference circuit for converting the servo control signal and the voltage generated by the master drive into a DC. reference voltage of opposite polarity, and wherein said control circuit includes electro-respon sive means having a control element for supplying a variable direct exciting current to said coupling, and wherein said excitation adjusting means includes means for applying the compared differential DC. voltage to the control element to vary the excitation of the coupling.

4. The system of claim 1 wherein said individual volttage generating means includes a pair of tachometer generators each independently coupled to the master and slave drive respectively, and wherein said voltage comparing means includes a governing circuit coupled to the output of the slave'tachometer generator and a reference circuit coupled to the master drive tachometer generator, and wherein said last-mentioned means includes circuit means for electrically coupling the servo system control signal to the reference circuit in algebraic relation to the voltage generated by the master drive tachometer generator.

5. The system of claim 1 wherein said brake excitation circuit includes eleotro-responsive means for supplying a direct exciting current to said brake, circuit means normally supplying an operating potential to said electroresponsive means, and wherein said brake disabling means includes circuit means for converting the coupling excitation into a controlpotential opposing said brake operating potential in said operating potential supply circuit, thereby rendering said electro-responsive means incorporative during excitation of the coupling.

6. In a system having a variable speed master drive and a slave drive adapted to be coupled to a load and including an electro-magnetic coupling between the slave and the load having a control circuit for adjustably exciting the coupling to maintain the slave output in synchronism with the master the combination comprising, individual means for generating a voltage proportional to the output speed of each drive respectively, means in said control circuit for comparing the generated voltages, other means in said control circuit for adjusting the excitation of said coupling in accordance with the compared differential between said generated voltages to provide a coarse speed matching, a servo system coacting between the drives to provide a control signal corresponding to minute differences in output speed between the drives, said servo system including a pair of servo-generators and means for independently coupling each to the output of the master and slave drives respectively, a differential selsyn motor coacting between the stator windings of the servo-generators to convert the minor differences between the output speeds of the master and slave drives into a corresponding mechanical movement, mechanically adjustable means for algebraically adding a variable voltage to the voltage generated proportional to the output speed of the master, and means for applying the mechanical movement from the differential motor to said mechanically adjustable means to adjust the variable voltage in accordance with the difference in output speeds of the drives and thereby synchronize the output of the slave with the output of the master drive.

7. The system of claim *6 wherein said servo generator coupling means includes means for selectively exciting each servo generator in response to a predetermined minimum differential between the drive-generated voltages.

8. The system of claim 6 wherein said excitation control circuit includes electro-responsive means having a control element for supplying a variable direct exciting current to the coupling, and wherein said voltage comparing means includes a governing circuit for converting the voltage generated by the slave drive into a DC. control voltage and a reference circuit for converting the combined servo control signal and the voltage generated by the master drive into a DC. reference voltage of op posite polarity, and wherein said excitation adjusting means includes means for applying the compared differential DC. voltage to the control element to vary the excitation of the coupling, and wherein said servo-generator coupling means includes means for selectively exciting the servo-generators in response to a predetermined minimum differential voltage applied to the control element.

9. 'In a system having a variable speed master drive and a slave drive adapted to be coupled to a load and including an electro-magnetic coupling coacting between the slave and the load and an electro-magnetic brake coacting with the slave, the coupling and brake each having a controlled excitation circuit to maintain the slave output in synchronism with the master the combination comprising, means normally activating the brake, other means operative in response to excitation of the coupling to disable the brake activating means, individual means for generating a voltage proportional to the output speed of each drive respectively, means in said control circuit for comparing the generated voltages, other means in said control circuit for adjusting the excitation of said coupling in accordance with the compared differential between said generated voltages to provide a coarse speed matching, a servo system coacting between the drives to provide a control signal corresponding to minute differences in output speed between the drives, said servo system including a pair of servo-generators and means for independently coupling each to the output of the master and slave drives respectively, a differential selsyn motor coacting between the stator windings of the servo-generators to convert the minor differences between the output speeds of the master and slave drives into a corresponding mechanical movement, mechanically adjustable means for algebraically adding a variable voltage to the voltage generated proportional to the output speed of the master, and means for applying the mechanical movement from the differential motor to said mechanically adjustable means to adjust the variable voltage in accordance with the difference in output speeds of the drives and thereby synchronize the output of the slave with the output of the master drive.

10. The system of claim 9 wherein said servo-generator coupling means includes means for selectively exciting the servo-generators in response to a predetermined minimum differential between the drive-generated voltages.

11. In combination, a variable speed master drive for supplying sheet material from a first supply roll to a work station, a slave drive for supplying sheet material from another supply roll in synchronism with the material from the first roll, said slave drive having an electromagnetic brake and an electro-magnetic coupling to said other supply roll, said coupling and said brake each having a controlled excitation circuit to maintain the slave output in synchronism with the master, other means operative in response to and during excitation of the coupling to disable the brake excitation circuit, individual means for generating a voltage proportional to the output speed of each drive respectively, means in said coupling excitation circuit for comparing the generated voltages, other means in said coupling excitation circuit for adjusting the excitation of the coupling in accordance with the compared ditferential voltage between said generated voltages to provide a coarse speed matching of the drives, a servo system coacting between the drives to provide a signal proportional to minute differences in speed between the drives, means for algebraically adding said signal to the voltage generated proportional to the output speed of the master drive and thereby superimpose a fine adjustment on said excitation adjustment means to synchronize the output of the slave with the master.

Harris Oct. 19, 1948 Jaescke May 1, 1956 

1. IN A SYSTEM HAVING A VARIABLE SPEED MASTER DRIVE AND A SLAVE DRIVE ADAPTED TO BE COUPLED TO A LOAD AND INCLUDING AN ELECTRO-MAGNETIC COUPLING BETWEEN THE SLAVE AND THE LOAD AND AN ELECTRO-MAGNETIC BRAKE FOR THE SLAVE, THE COUPLING AND THE BRAKE EACH HAVING A CONTROLLED EXCITATION CIRCUIT TO MAINTAIN THE SLAVE OUTPUT IN SYNCHRONISM WITH THE MASTER, THE COMBINATION COMPRISING, MEANS CONDITIONING THE BRAKE EXCITATION CIRCUIT TO CONTINUOUSLY ACTIVATE THE BRAKE, OTHER MEANS OPERATIVE IN RESPONSE TO AND DURING EXCITATION OF THE COUPLING TO DISABLE THE BRAKE EXCITASTION CIRCUIT, INDIVIDUAL MEANS FOR GENERATING A VOLTAGE PROPORTIONAL TO THE OUTPUT SPEED OF EACH DRIVE RESPECTIVELY, MEANS IN SAID COUPLING EXCITATION CIRCUIT FOR COMPARING THE GENERATED VOLTAGES, OTHER MEANS IN SAID COUPLING EXCITATION CIRCUIT FOR ADJUSTING THE EXCITATION OF THE COUPLING IN ACCORDANCE WITH THE COMPARED DIFFERENTIAL VOLTAGE BETWEEN SAID GENERATED VOLTAGES TO PROVIDE A COURSE SPEED MATCHING OF THE DRIVES, A SERVO SYSTEM COACTING BETWEEN THE DRIVES TO PROVIDE A SIGNAL PROPORTIONAL TO MINUTE DIFFERENCES IN SPEED BETWEEN THE DRIVES, MEANS FOR ALGEBRAICALLY ADDING SAID SIGNAL TO THE VOLTAGE GENERATED PROPORTIONAL TO THE OUTPUT SPEED OF THE MASTER DRIVE AND THEREBY SUPERIMPOSE A FINE ADJUSTMENT ON SAID EXCITATTION ADJUSTMENT MEANS TO SYNCHRONIZE THE OUTPUT OF THE SLAVE WITH THE MASTER. 